BACKGROUND OF THE INVENTION
[0001] The present invention relates to a crushing apparatus and a crushing method according
to the pre-characterizing part of claims 1 and 5 respectively.
[0002] In the prior art, it is known to preliminarily coarsely crush materials to be crushed
such as cement clinker, cement material, slug, ores and the like by utilizing a vertical
roller mill which is excellent in coarse crushing efficiency. The thus coarsely crushed
materials are thereafter finely crushed by utilizing a tube mill, for example, which
is excellent in fine crushing efficiency.
[0003] Examples of such prior art are disclosed in EP-A-0 054 344 and in the Japanese Patent
Laid-Open Publication No. 238349/1986, which is shown in Fig. 10.
[0004] Fig. 10 shows a schematic diagram of a crushing apparatus for crushing materials
such as cement clinker and referring to Fig. 10, materials to be crushed fed into
a vertical roller mill 2 through a material feed port 1 are coarsely crushed in the
vertical roller mill 2. The crushed materials are then fed towards a separator 4 through
a bucket elevator 3. The coarsely crushed materials classified in the separator 4
in accordance with the sizes of the materials are guided into a tube mill 5 in which
the coarsely crushed materials are further crushed finely. The finely crushed materials
are returned to the separator 4 through the bucket elevator 3. The finely crushed
materials returned to the separator 4 are again classified and then taken out as products
through a chute 6. Dust is collected by a dust collector.
[0005] Such crushing apparatus as shown in Fig. 10 may be called "one-pass crushing apparatus"
because one crushing process is performed by the vertical roller mill 2. In such one-pass
crushing apparatus, the materials to be crushed are coarsely crushed in the vertical
roller mill 2, and for example, cement clinker having a grain size of 50 mm to 1 mm
is crushed to grains having a size of 15 mm to 0.01 mm. The vertical roller mill 2
generally includes a table rotatable around its perpendicular axis and a plurality
of rollers arranged on the table in a circumferentially spaced relationship.
[0006] The materials are fed through the inlet port 1 on substantially the central portion
of the table of the vertical roller mill 2 and then crushed in a gap between the rotating
table and the rollers by biting the materials in the gap and then applying pressure
to the rollers. For this crushing operation, a perpendicularly downwards-acting large
pressing force is applied to the rollers by a pressing means such as hydraulic cylinder
means thereby causing large pressing force between the rollers and the table.
[0007] Accordingly, in the utilization of the vertical roller mill of the structure described
above, large vibration is generated irrespective of the sizes of the materials to
be crushed. The generation of such large vibrations constitutes a significant problem
for persons who design the crushing apparatus to reduce them to as small as possible.
[0008] In a case where such vertical roller mill 2 is utilized as an apparatus for preliminarily
crushing materials, it will be initially required for the vertical roller mill to
crush materials of relatively large grain sizes and to effectively crush the same
in substantially one crushing process. Because of such requirements, it will be necessary
for such a vertical roller mill to have a large pressing force or power in comparison
with a generally utilized vertical roller mill.
[0009] Namely, since the materials fed into the vertical roller mill 2 contain materials,
which in percentage, are coarse and have relatively large sizes, it is therefore necessary
to effectively crush the materials with a reduced crushing operation time, resulting
in the requirement of large pressing force.
[0010] As described above, therefore, since the vertical roller mill utilized as the preliminarily
crushing means generates large vibrations when compared with a usual vertical roller
mill, in the actual operation, it is necessary for the preliminarily crushing type
vertical roller mill to be operated with pressing force of the rollers at a value
considerably lower than a desired value for the effective crushing operation, thus
providing an important problem. In addition, in a mechanical point of view, an additional
attention have to be paid for vibration-proof design, thus being not economical.
[0011] Furthermore, materials to be newly crushed usually have various sizes, properties
such as physical characteristics and the like, and these materials will be continuously
fed in the actual crushing operation. Such variations or changes of the sizes and
properties of the newly fed materials directly affect a one-pass crushing apparatus
of the vertical roller mill type shown in Fig. 10.
[0012] Thus, in a case where materials having different sizes are fed, the vibration level
or degree will change, and in association therewith, the driving capacity of the vertical
roller mill has to be changed, thus also providing a troublesome problem.
[0013] In a case where materials having different properties are fed and materials which
are hardly crushed are fed, the crushing capacity of a crushing plant is degraded,
so that an amount of the material to be supplied to the vertical roller mill is reduced,
and hence, the thickness of the materials to be taken into the gap between the rollers
and the table of the vertical roller mill is also reduced. As a result, the vibration
level will increase and the crushing capacity of the crushing plant will be further
degraded. On the contrary, when materials relatively easily crushed are fed, the crushing
capacity of the crushing plant can be increased, so that the material thickness between
the rollers and the table is also increased, resulting in a decrease of the vibration
level. However, in this case, since the material thickness increases, a pressure receiving
area of the materials for receiving the roller pressure is increased, so that the
press crushing force to be applied to a unit area will be substantially reduced, resulting
in the lowering of the actual crushing efficiency.
[0014] As described above, according to the so-called one-pass crushing apparatus, the grain
sizes and the properties of the materials to be crushed directly affect thereon, so
that the crushing apparatus cannot always be operated under optimum constant and stable
crushing conditions.
[0015] Fig. 11 represents another example of the prior art such as disclosed in the Japanese
Patent Laid-Open Publication No. 116751/1988. Fig. 11 shows a schematic diagram of
a crushing apparatus, and referring to Fig. 11, materials fed through a material feed
inlet port 8 into a vertical roller mill 9 are once preliminarily or primarily crushed
therein and the crushed materials are conveyed to a screening device 11 through a
bucket elevator 10. The preliminarily crushed materials are screened by a screening
surface 12 of the screening device 11, and the coarse materials in the materials fed
from the vertical roller mill 9 each having a grain size larger than a predetermined
size more than 2.5 mm, for example, are separated in the screening device 11 and then
returned to the vertical roller mill 8 through a chute 13 for re-crushing the coarse
materials.
[0016] On the contrary, relatively finely crushed materials separated from the coarse materials
described above are conveyed to a tube mill 15 through a chute 14 for secondary fine
crushing operation. The materials finely crushed by the tube mill 15 are classified
by a separator in accordance with their grain sizes, and the materials each having
a grain size larger than a predetermined value are again returned to the tube mill
15 for re-crushing the same. The fine materials not returned to the tube mill 15 are
taken out therefrom as products through a chute 17. A crushing apparatus of such a
type may be called a screening re-circulation type of crushing apparatus because of
its nature.
[0017] The latter mentioned prior art crushing apparatus aims, in comparison with the former
mentioned prior art crushing apparatus, to improve the crushing efficiency of the
tube mill, that is, to feed the crushed materials of further small grain sizes to
the tube mill by screening the coarse materials, each having a grain size more than
the predetermined size such as 2.5 mm, once crushed by the vertical roller mill and
returned again to the vertical roller mill for the re-crushing thereof.
[0018] However, in the latter mentioned screening re-circulation type crushing apparatus,
since the materials once crushed but each having grain size of more than a predetermined
value such as more than 2.5 mm are returned to the vertical roller mill 9, the grain
sizes of the materials in the vertical roller mill 9 are not substantially changed
even after the preliminarily or primarily crushing operation therein. In other words,
even in the screening re-circulation type crushing apparatus, the problem of causing
large vibrations during the crushing operation is not solved, as is caused in the
one-pass type crushing apparatus.
[0019] In addition, in the screening re-circulation type crushing apparatus, the influences
caused by the change of property of newly fed materials to be crushed in the vertical
roller mill are given more largely to the vertical roller mill than the case of the
one-pass type crushing apparatus. These influences will be also imparted proportionally
to the entire operation of a plant, thus increasing the possibility of instable crushing
operation thereof.
[0020] Namely, in this crushing apparatus, the materials once crushed by the vertical roller
mill are separated into coarse and relatively fine ones by the screening device, the
coarse ones then being returned to the vertical roller mill and the fine ones being
fed to the tube mill for the secondary finely crushing operation.
[0021] Accordingly, amounts of the coarse and fine materials after the screening operation
are decided by the grain sizes of the materials crushed by the vertical roller mill.
As a matter of nature, the grain sizes of the materials to be fed into the vertical
roller mill are not usually constant, and in addition to this fact, the returned coarse
materials to the vertical roller mill varying in their amount are continuously added
to and mixed with the materials newly fed into the vertical roller mill.
[0022] Accordingly, the total amount in the vertical roller mill always changes and this
fact magnifies the change of the property of the materials to be crushed in the vertical
roller mill as well as the changes of their grain sizes. This will be applied even
to a case where the feeding amount of the materials to be newly fed into the vertical
roller mill is relatively constant.
[0023] Consequently, the magnitude of vibrations of the vertical roller mill always change,
as well as the amount of electric power consumption for the vertical roller mill.
[0024] Furthermore, since the amount of the secondary separated fine materials to be fed
to the tube mill 15 always varies in size, the tube mill 15 cannot be constantly stably
operated. Namely, in the screening re-circulation type crushing apparatus of the conventional
type described above, the circulation amount of the materials to the vertical roller
mill 9 and the supply amount thereof to the tube mill 15 are not optimumly controlled
in accordance with the change of properties of materials to be newly fed.
[0025] Furthermore, in a crushing plant such as for crushing cement clinker, the crushing
capacity is usually of 100 ton/hour to 150 ton/hour, and when materials of such an
amount are subjected to screening treatment, materials of about 130 to 200 ton including
the circulation amount must be treated per one hour, thus requiring the screening
device to have a considerably large size and treating capacity. It is also difficult
to use the screening net means for a long time, as it is uneconomical and troublesome
to maintain.
[0026] An apparatus and a method according to the precharacterizing part of claims 1 and
5 are known from EP-A-0 352 192 and DD-A-226 278, respectively.
[0027] The object of the present invention is to provide an apparatus and method for crushing
materials by utilizing a vertical roller mill capable of possibly reducing vibrations
of the vertical roller mill caused during the material crushing operation and achieving
an optimum material press crushing force.
[0028] This object is accomplished by the features of claims 1 and 5, respectively.
[0029] The present invention provides an apparatus and method for crushing materials such
as cement clinker by utilizing a vertical roller mill capable of reducing vibrations
of the vertical roller mill caused during the material crushing operation and achieving
always stable operation of the vertical roller mill even in consideration of changes
in grain sizes and properties of the materials to be fed in and crushed by the vertical
roller mill.
[0030] In a preferred embodiment, the crushing apparatus may further comprise a detector
for detecting a consuming power of the driving means for driving the table of the
vertical roller mill and a control circuit connected to the detector, the control
circuit being connected to the pressing means, wherein a pressing force of the pressing
means to the rollers is controlled by the control circuit in accordance with the consuming
power of the motor.
[0031] In the crushing method, the return amount of the crushed materials from the distributing
device is controlled in accordance with a consuming power of the rotatable table of
the vertical roller mill, and the pressing force of the roller means is controlled
in accordance with a consuming power of the rotatable table of the vertical roller
mill.
[0032] In the present embodiments, cement clinker is preferably utilized as the material
to be crushed.
[0033] According to the present invention of the characters described above, the crushing
apparatus includes a vertical roller mill for preliminarily or primarily crushing
materials. The materials fed into the vertical roller mill enter into a gap between
the rollers and the table of the vertical roller mill and are crushed by pressing
force applied to the rollers. Substantially the whole amount of this crushed material
is taken out from the vertical roller mill and then conveyed to the distributing device.
In the distributing device, the materials are distributed as they are and a portion
of the materials is returned to the vertical roller mill. The returned materials and
the materials newly fed into the vertical roller mill are again crushed thereby increasing
the bulk density of the materials to be crushed between the table and the rollers
of the vertical roller mill to reduce the percentage of void of the materials.
[0034] Accordingly, the magnitude of vibrations of the vertical roller mill caused during
the material crushing operation can be remarkably reduced and the crushing operation
can be performed by the optimum pressing force of the rollers, thus achieving the
improved crushing efficiency. The reduction of the vibrations of the vertical roller
mill may result in the simple and compact structure thereof, thus being economical.
The consuming power of the vertical roller mill can be remarkably increased, thus
improving the crushing capacity thereof, and the bulk density of the materials to
be crushed is also increased, thus reducing the rolling resistance of the rollers,
resulting in the improvement of the crushing efficiency.
[0035] In addition, the returning amount of the crushed materials from the distributing
device is controlled in accordance with the power consumption of the rotatable table
of the vertical roller mill, and the pressing force of the rollers is controlled in
accordance with a power consumption of the rotatable table of the vertical roller
mill. Accordingly, the material crushing operation can be performed with the optimum
press crushing force of the rollers.
[0036] In the preferred embodiment, when the cement clinker is utilized as materials to
be crushed, the crushing efficiency can be remarkably improved by returning, again
to the vertical roller mill, the materials once crushed in the vertical roller mill
and conveyed in the distributing device by about 20% or more, in weight ratio, with
respect to the materials to be newly fed into the vertical roller mill because in
such case, the bulk density of the materials can be always maintained high.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] For a better understanding of the present invention and to show how the same is carried
out, reference is first made, by way of preferred embodiments, to the accompanying
drawings, in which:
Fig. 1 is a schematic diagram of a first embodiment of a crushing apparatus according
to the present invention;
Fig. 2 is an elevational view partially in section of a vertical roller mill of the
crushing apparatus of Fig. 1;
Fig. 3 is a brief sectional view of a distributing device of the crushing apparatus
of Fig. 1;
Fig. 4 is a view for the explanatory of the crushing operation between a table and
rollers of the vertical roller mill of Fig. 2;
Fig. 5 is a graph showing relationship of a bulk density of cement clinker powder
with respect to a powder mixing ratio;
Fig. 6 is a schematic diagram similar to that of Fig. 1, but showing a second embodiment
according to the present invention;
Fig. 7 is a graph for the explanatory of an operation of a control circuit of the
crushing apparatus of Fig. 6;
Fig. 8 is a schematic diagram similar to that of Fig. 1 or 6, but showing a third
embodiment according to the present invention;
Fig. 9 is a graph for the explanatory of an operation of a control circuit of the
crushing apparatus of Fig. 8; and
Figs. 10 and 11 are schematic diagrams of two examples of crushing apparatus of prior
art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] Fig. 1 is a schematic diagram showing one embodiment according to the present invention.
[0039] Referring to Fig. 1, in this embodiment, it is assumed that cement clinker is treated
as the material to be crushed. The cement clinker is fed from a material feed hopper
18 by a predetermined constant amount per unit time by means of a constant amount
feeder 19 and fed, by means of a chute 20, into a vertical roller mill 21 through
an inlet port 22 thereof. The vertical roller mill 21 comprises a table member 34
disposed substantially horizontally and a plurality of rollers 38 arranged above the
peripheral portions of the table 34. Substantially all of the materials fed into and
preliminarily or primary coarsely crushed by the vertical roller mill 21 is taken
out through a chute 24 having one end disposed at a portion below the table 34 of
the vertical roller mill 21.
[0040] The crushed materials taken out from the vertical roller mill 21 through the chute
24 are conveyed by a bucket elevator 25 into a distributing device 26 installed at
the upper part of the bucket elevator 25, by which a portion of the crushed materials
from the vertical roller mill 21 is returned, as it is, to the inlet port 22 thereof
through a chute 27. And the remainder thereof is fed through a chute 28 into a tube
mill 29 installed downstream the vertical roller mill 21 for carrying out a secondary
crushing operation therein. The tube mill 29 is of a horizontal structure comprising
a drum body having a horizontal axis in which a crushing means is disposed. The materials
finely crushed by this crushing means of the tube mill 29 are guided to a separator
such as an air separator 31 through a bucket elevator 30. In the separator 31, the
crushed materials are classified in accordance with their grain sizes and the coarsely
crushed materials are again returned through a chute 32 to the tube mill 29 for the
re-crushing operation therein. The finely crushed materials separated in the separator
31 are then taken out as products through a chute 33.
[0041] Fig. 2 is a sectional view of the vertical roller mill 21 as shown by arrow A in
Fig. 1 in an enlarged scale. The vertical roller mill 21 is disposed substantially
horizontally in a housing 37 and includes the table 34 having a perpendicular axis.
The table 34 is driven to be rotated about the axis by means of a motor 35 and a speed
reduction device 36. In the housing 37, there is also arranged a plurality of, three,
for example, rollers 38 which are driven by a pressing device such as hydraulic cylinder
means 39 so as to be press contacted to the surface of the table 34. The rollers 38
are supported by arms 40 which are angularly separated in positions about support
shafts 41, respectively, thereby pressing the rollers 38 against the surface of the
table 34. The material inlet port 22 is disposed to the upper portion of the housing
37 at substantially the central portion thereof. The inlet port 22 is also communicated
with a chute 42 disposed in the housing 37 substantially coaxially with the perpendicular
axis of the table 34 so that the materials fed through the inlet port 22 are fed at
substantially the central portion of the table surface. There exists a circumferential
gap 43 between the outer peripheral surface of the table 34 and an inner wall of the
housing 37, and the materials crushed between the table 34 and the rollers 38 are
fed through this gap 43 into the chute 24 and then to the bucket elevator 25.
[0042] Fig. 3 is an elevational section of a distributing device 26, as shown by arrow B
in Fig. 1, which is operatively connected to the bucket elevator 25. Referring to
Fig. 3, the materials crushed in the vertical roller mill 21 are fed into the distributing
device 26 through the bucket elevator 25 from the upper portion of a housing 44 of
the distributing device 26. The lower portion of the housing 44 is separated into
two parts, one being connected to the chute 27 communicated to the vertical roller
mill 21 and the other being connected to the chute 28 communicated to the tube mill
29. At the central portion of these two portions there is disposed a shaft 45 having
a horizontal axis, and a distributing vane 46 is mounted to the shaft 45 changeable
in its inclination as shown by an arrow 47a. The distributing vane 46 is operated
by a distributing vane driving means 47 so that the vane 46 can be set to a position
having a desired inclination. The amount or ratio of the materials crushed by the
vertical roller mill 21 and to be distributed to the chutes 27 and 28 can be adjusted
by changing the inclination angle of the distributing vane 46. Merits and advantages
caused by these structures will be understood by the following disclosures for solving
the problems encountered in the conventional apparatus.
[0043] First, the reason why the vertical roller mill 21 for preliminarily crushing the
materials generates a large vibration will be explained by taking into consideration
one example in which cement clinker is used as the material to be crushed.
[0044] With reference to Fig. 4 schematically showing the crushing mechanism including the
table 34 and the rollers 38, when the table 34 is rotated about its perpendicular
axis, the materials 48 to be crushed on the table 34 enter, i.e. are taken, between
the rollers 38 and the table 34 and crushed by the pressing force of the rollers 38.
A bulk density G1 of the clinker before taking between the table 34 and the rollers
38 is usually about 1.5 and a bulk density G2 after the crushing of the cement clinker
is about 2.5.
[0045] Accordingly, assuming that a thickness of the clinker layer before the crushing is
T and that after the crushing is t, an equation T/t = 1.67 will be obtained. That
is, the layer thickness change amount ΔT (= T-t) is 0.4T. The vertical roller mill
usually utilized for the preliminary crushing of the cement clinker has a crushing
capacity to crush the cement clinker so as to have a thickness
t of about 30 mm. Accordingly, the thickness of the cement clinker before crushing
T is assumed to be about 50 mm and the layer thickness change is to be about 20 mm.
The periphery of the table 34 is usually rotated with a rotating speed of about 3.5
m/sec, being relatively large, and since the cement clinker on the table 34 is rotated
and taken in under such large rotating speed of the table 34, the layer change amount
ΔT frequently changes violently in response to the change of properties such as physical
characteristics of the cement clinker and the amount of the cement clinker to be crushed.
According to such changes, the rollers 38 violently change their vertical positions,
resulting in the generation of large abnormal magnitude of vibrations.
[0046] In the prior art, in order to eliminate such vibrations, it was attempted to lower
the downward pressing force of the rollers and to lower the rotating speed of the
table thereby reducing the taking in speed to the rollers. However, in the former
attempt, the lowering of the pressing force of the rollers results in a lowering of
the crushing efficiency. The power consumption of the vertical roller mill also decreases
and accordingly, a larger vertical roller mill is required to obtain the same crushing
capacity. However, in the latter attempt, the power consumption of the vertical roller
mill also decreases, so that a larger vertical roller mill is hence disadvantageously
required.
[0047] Taking the above technical matters into consideration, the inventors of the subject
application were considered that the most effective structure of the vertical roller
mill for the preliminary crushing for significantly reducing the vibrations thereof
should be designed so as to make small the material layer thickness change amount
ΔT.
[0048] Namely, since the new materials to be crushed such as clinker are mainly composed
of coarse grains, the percentage of voids is large and bulk density is small. Accordingly,
such materials are pressed and crushed, the volume thereof is remarkably reduced,
and hence, the material layer thickness is largely changed. The inventors were therefore
considered to make large the bulk density of the materials to be bitten and crushed
between the table and the rollers and carried out various investigations.
[0049] As this result, it was concluded to be most effective that the materials to be preliminarily
crushed by the vertical roller mill are not to be separated into fine materials and
coarse materials and that these preliminarily crushed materials be mixed as they are
with new materials such as cement clinker.
[0050] Assuming that the materials to be crushed of the layer thickness T have a bulk density
G1 and the materials of the layer thickness t have a bulk density G2, the following
equations will be obtained.
and accordingly,
[0051] Accordingly, it will be found that in order to reduce the amount of layer thickness
change, it is desired to increase the bulk density G1 of the materials to be crushed
by the vertical roller mill.
[0052] The results of experiments carried out by the inventors will be described hereunder.
[0053] Fig. 5 is a graph showing a relationship between the mixing ratio R and the bulk
density G of powder material to be supplied to the vertical roller mill 21, based
on the experiments, in which the value R is represented as follows.
in which the symbol W1 represents the weight of cement clinker as new materials to
be fed into the vertical roller mill 21 through the chute 20 and crushed therein and
the symbol W2 represents the weight of cement clinker as materials to be fed again
into the vertical roller mill 21 through the chute 27 from the distributing device
26. In Fig. 5, a solid line L1 shows a characteristic feature in a case of the cement
clinker fed and mixed in the vertical roller mill 21 through the chute 27 being the
one-pass crushed materials, i.e. preliminarily crushed materials, a solid line L2
shows a characteristic feature in a case of the cement clinker fed and mixed in the
vertical roller mill 21 through the chute 27 after the distribution in the distributing
device 26 being the preliminarily crushed materials each having a grain size of more
than 2.5 mm, and a dotted line L3 shows a characteristic feature in a case of minute
powders each having a powder size of less than 300 µm being fed and mixed in the vertical
roller mill through the chute 27.
[0054] As represented by the line L2, in the case of the materials of each grain size being
more than 2.5 mm, the bulk density thereof has a low value substantially equal to
the bulk density of 1.61 of the cement clinker itself regardless of the mixing ratio
R. Accordingly, it will be understood that problems caused in the case of the one-pass
crushing apparatus will be also caused in the case of the screening re-circulation
crushing apparatus as described hereinbefore with reference to Fig. 11.
[0055] As represented by the line L3, in the case of fine powders each having a powder size
less than 300 µm being mixed, the bulk density G increases till the mixing ratio of
the fine powders becomes 40%, but when the mixing ratio R further increases, with
the peak of 40%, the bulk density G decreases. Accordingly, when only fine powder
materials are mixed, tee operating condition of the vertical roller mill 21 is made
instable when the mixing ratio is changed.
[0056] On the contrary, as represented by the line L1, in the case of the preliminarily
crushed materials being mixed as they are, the bulk density G increases to a value
1.95 from a value 1.55 till the mixing ratio R becomes 20% and is maintained to a
large value of about 2.1 in the mixing ratio R more than 20%. Accordingly, it will
be found that it is remarkably effective for solving the problems caused in the prior
art to mix the preliminarily crushed materials as they are, with the new materials
fed into the vertical roller mill.
[0057] As is apparent from Fig. 5, according to the present invention, as represented by
the line L1, it was evidenced in the experiments of the inventors that the bulk density
of the materials to be crushed by the vertical roller mill 21 is made large when the
mixing ratio is more than about 20%, preferably more than 25%, and the magnitude of
vibrations of the vertical roller mill 21 can be therefore effectively reduced at
that mixing ratio. Furthermore, the bulk density of a relatively large value is maintained
constantly at a mixing ratio R of more than about 40%. Accordingly, in this range,
even if the property of the clinker fed through the chute 20 can be changed, the bulk
density thereof in the vertical roller mill 21 is maintained substantially constant,
so that the vibrations may be effectively suppressed.
[0058] Therefore, according to the embodiment represented by the apparatus shown in Fig.
1, the vibrations of the vertical roller mill 21 can be remarkably reduced only by
returning, by a predetermined constant amount, the materials preliminarily crushed
by the vertical roller mill 21 and distributed in the distributing device 26. Thus,
an optimum roller pressing force can be applied for the crushing of the materials
in the vertical roller mill 21 with increasing driving efficiency, and an improved
crushing capacity can be realized with substantially no design change of the vertical
roller mill.
[0059] Furthermore, as shown in Fig. 3, the amount of re-circulation of the materials to
the vertical roller mill 21 from the distributing device 26 can be optionally adjusted
by changing the degree of opening inclination of the distributing vane 46 disposed
in the distributing device 26, whereby even in a case where the operating condition
be changed in accordance with the property of the new materials to be crushed, the
operating condition can be maintained to be constant by changing the re-circulation
amount of the materials from the distributing device 26. The distributing device 26
has itself a relatively simple and compact structure.
[0060] The crushed materials to be fed to the tube mill 29 can be also adjusted to be constant
in amount, thus the tube mill 29 can be also maintained stably in its operating condition.
[0061] As described hereinbefore, according to the first embodiment of the present invention,
the problems encountered in the prior art can be effectively solved by a crushing
apparatus having a relatively simple structure and the effects and advantages thereof
were confirmed by the experiments of the inventors.
[0062] In the described embodiment, when materials difficult to be crushed are newly fed
and the crushing capacity of the crushing apparatus is decreased, the new materials
to be fed to the vertical roller mill 21 will be reduced in amount, and as the result,
the amount of the preliminarily crushed materials taken out from the vertical roller
mill 21 is also reduced. In such case, when the distributing device 26 maintains its
distributing ratio constant, the re-circulation amount of the materials to the vertical
roller mill 21 from the distributing device 26 is also reduced. As the result, the
total amount of the materials to be fed to the vertical roller mill 21 is hence reduced,
thus reducing the power consumption, as well as the crushing efficiency.
[0063] On the contrary, when materials easily crushed are newly fed and the crushing capacity
of the crushing apparatus is increased, the new materials to be fed to the vertical
roller mill 21 will be increased in amount. In such a case, when the distributing
device 26 maintains its distributing ratio to be constant, the re-circulation amount
of the materials to the vertical roller mill 21 from the distributing device 26 is
also increased.
[0064] As the result, the total amount of the materials to be fed to the vertical roller
mill 21 is hence increased, thus reducing the consuming power of the motor 35 being
increased. If the vertical roller mill 21 is operated till this time with the rated
value of the motor 35, the increasing of the amount of the materials to be crushed
may result in the increasing of the consuming power of the vertical roller mill 21,
which may cause an overload of the motor 35, and being dangerous for the motor operation.
[0065] Accordingly, in the foregoing first embodiment, it may be required to locate the
motor 35 having a relatively large capacity with respect to the consuming power of
the utilized vertical roller mill, and furthermore, since the power consumption of
the vertical roller mill is naturally changed in accordance with the property change
of the materials to be crushed, the change of the crushing capacity of the entire
crushing apparatus may be increased accordingly, thus being inconvenient.
[0066] A second embodiment of the present invention is provided for effectively improving
the above defects of the first embodiment and will be described hereunder with reference
to Figs. 6 to 7.
[0067] Fig. 6 is a schematic diagram showing the second embodiment according to the present
invention, in which like reference numerals are added to members and devices corresponding
to those of the first embodiment shown in Figs. 1 to 5. In the second embodiment with
reference to Fig. 6, it is attempted to make power consumption of the vertical roller
mill 21 always constant by automatically deciding the distributing ratio of the distributing
device 26 on the basis of the consuming power of the driving motor 35 of the vertical
roller mill 21. The power consumption of the motor 35 driving the table 34 of the
vertical roller mill 21 is detected by a power consumption detection means 51 and
the detected power is given to a control circuit 52, which controls a driving means
47 for driving the distributing vane 46 of the distributing device 26. The structure
other than these structures of the crushing apparatus of the second embodiment is
substantially identical to those of the first embodiment.
[0068] Fig. 7 is a graph for describing the operation of the crushing apparatus shown in
Fig. 6. Referring to Fig. 7, when the new materials to be fed through the chute 20
in the vertical roller mill 21 and crushed therein are increased in the amount, the
consuming power of the motor 35 detected by the detecting means 51 is increased as
shown by a solid line L4. In response to this fact, the control circuit 52 controls
the driving means 47 to leftwardly, as viewed in Fig. 3, change the inclination of
the distributing vane 46, and according to this change, the re-circulation amount
of the materials from the distributing device 26 towards the vertical roller mill
21 is reduced as shown by a solid line L5. By virtue of such operation, the power
consumption of the motor 35 for the vertical roller mill 21 can be maintained to be
constant as shown by a dotted line L6.
[0069] According to the second embodiment represented by Figs. 6 and 7, in a case where
the power consumption of the vertical roller mill 21 changes in accordance with the
property change of the materials to be crushed, for example, when the power consumption
of the vertical roller mill 21 is reduced and the consuming power of the motor 35
is hence reduced, the control circuit 52 automatically controls the distribution ratio
of the distributing device 26 in response to the reduction rate of the consuming power
so as to automatically increase the returning amount of the materials towards the
vertical roller mill 21.
[0070] Accordingly, the total amount of the materials to be fed to the vertical roller mill
21 is increased, and as this result, the power consumption of the vertical roller
mill 21 returns to its original value. On the contrary, when the power consumption
of the vertical roller mill is increased and the power consumption of the motor 35
is hence increased, the control circuit 52 automatically controls the distributing
ratio of the distributing device 26 in response to the increased rate of the consuming
power so as to automatically reduce the returning amount of the materials towards
the vertical roller mill 21. Accordingly, the total amount of the materials to be
fed to the vertical roller mill 21 is reduced, and as this result, the power consumption
of the vertical roller mill 21 returns to its original value.
[0071] As described above, according to the present embodiment, the power consumption of
the vertical roller mill 21 can be always constantly maintained regardless of the
property of the materials to be crushed and the consuming power of the vertical roller
mill 21 can be optimumly decided, so that it is not necessary to arrange the motor
35 having a capacity more than necessity and the waving of the crushing capacity can
be significantly suppressed, thus being effective and advantageous.
[0072] Namely, according to this second embodiment, the power consumption of the vertical
roller mill 21 performing the preliminary crushing can be easily maintained constantly
regardless of the property change of the materials to be crushed and the change of
the crushing capacity of the crushing apparatus itself can be suppressed minimumly.
Thus, the operating condition of the crushing apparatus can be always stably maintained
with the far improved crushing efficiency. Furthermore, there is no need for the location
of the vertical roller mill driving motor 35 having a capacity more than necessity,
resulting in merits in construction cost.
[0073] In this embodiment, although the distributing rate of the distributing device 26
is automatically managed in accordance with the power consumption of the vertical
roller mill 21, the distribution rate may be controlled by other means such as remote
control means.
[0074] Figs. 8 and 9 further represent an embodiment according to the present invention
as the third embodiment, in which like reference numerals are added to members and
devices corresponding to those shown in Fig. 1 or 6.
[0075] In the third embodiment, a hydraulic cylinder assembly is utilized as the pressing
means 39 for pressing the rollers 38 of the vertical roller mill 21 preliminarily
crushing the materials, and the hydraulic pressure of the hydraulic cylinder assembly
39 is automatically changed by utilizing the power consumption of the motor 35 to
change the pressing force of the rollers 38 and hence thereby maintaining always constant
the power consumption of the vertical roller mill 21. The power consumption of the
motor 35 is detected by the detecting means 51 and the hydraulic cylinder assembly
39 is controlled by the control circuit 53. In order to achieve these purposes, as
shown in Fig. 8, the pressing means 39 is connected to the control circuit 53 and
the motor 35 is connected to the detecting means 51, which is operatively connected
to the control circuit 53.
[0076] Fig. 9 is a graph for describing the operation of the crushing apparatus of the third
embodiment shown in Fig. 8. When the materials to be fed to the vertical roller mill
21 from the constant amount feeder 19 through the chute 20 is increased in their amount,
the power consumption of the motor 35 to be detected by the detecting means 51 is
increased as shown by a solid line L7. At this time, the control circuit 53 is operated
in response to an output from the detecting means 51 thereby controlling the pressing
means 39, whereby the pressing force of the rollers 38 against the table 34 is reduced
as shown by a solid line L8. In thus manner, the power consumption of the motor 35
can be maintained constant as shown by a dotted line L9.
[0077] As will be understood from the above description of the third embodiment, this embodiment
is particularly suitable for the improvement of the second embodiment. Namely, in
the second embodiment, the power consumption of the vertical roller mill 21 is made
constant by changing or adjusting the amount of the materials returning to the vertical
roller mill 21 by changing the distributing rate of the distributing device 26. In
such case, there is the fear of temporarily changing the amount of the materials to
be fed to the tube mill 29 for the secondary crushing operation in accordance with
the changing of the amount of the materials returning to the vertical roller mill
21, which may cause a temporary disturbance to the operation condition on the side
of the tube mill 29 of the crushing apparatus.
[0078] According to the third embodiment, such problem of the second embodiment can be solved.
That is, the distributing rate of the distributing device 26 is maintained to be always
constant and the pressing force of the rollers 38 automatically changes with respect
to the changing of the consuming power of the motor 35 of the vertical roller mill
21 in accordance with the property change of the materials to be crushed, whereby
the consuming power of the vertical roller mill 21 can be maintained to be always
constant.
[0079] According to the structure of the third embodiment, since the materials can be always
fed to the tube mill 29 substantially stably even if the property of the materials
be changed, the operation condition on the side of the tube mill 29 never be disturbed
and can be maintained stably. In addition, the consuming power of the vertical roller
mill 21 can also be maintained constant. Therefore, the crushing apparatus can be
entirely stably operated with the optimum crushing performance and efficiency. To
make it possible to automatically change the pressing force of the rollers 38 may
be partially based on the fact that the magnitude of vibrations of the vertical roller
mill 21 can be significantly reduced by partially re-circulating the preliminarily
crushed materials again to the vertical roller mill 21.
[0080] Furthermore, it will be easily noted that the tube mill 29, the bucket elevator 30
and the separator 31 may be substituted with other means carrying out substantially
the same operations, and the present invention may be adapted to purposes other than
the preliminarily crushing operation for the tube mill 29.